1. Field of the Invention
The present invention relates to a motor, and more particularly, a motor in which a skew angle is changed according to a load condition so that generated noise and vibration can be reduced, as compared to a conventional one.
2. Description of the Prior Art
Cogging torque refers to a ripple type torque generated by an interaction between a rotor (magnet) and a stator (core) in a permanent magnet type motor, and includes forward and reverse torques generated according to a change of magnetic flux of the motor itself even if no current is input.
The cogging torque should be properly reduced since it causes ripple and noise when the motor is operated.
A conventional method for reducing the cogging torque is to apply a skew structure to the rotor or the stator so as to uniformize the change of magnetic flux caused by rotation of the rotor so that the forward and reverse torques are counterbalanced.
Here, skew refers to configuring a permanent magnet to have a magnetic phase difference in the circumferential direction. According to a structure of a motor, a skew structure is obtained, for example, by attaching a ring magnet to a rotor, forming a slot of a stator to be inclined, attaching segment-shaped magnets in a plurality of rows, or attaching an arc-shaped segment magnet to a rotor.
FIG. 1 is a view illustrating an example of a rotor and a stator, to which a magnet skew structure according to a prior art is applied.
As illustrated in FIG. 1, a stator 101 has a cylindrical shape with opened opposite ends, and a plurality of opened slots 103 are formed on the inner surface of the stator 101 at regular intervals along the circumferential. The slots 103 are formed to be separated from each other by slot tees 105, which protrude radially from the inner surface of the stator 101.
A rotor 107 includes segment-shaped magnets 109 and 111, which are attached in vertically two stages, in which the magnets 109 of the upper stage are arranged to deviate from the magnets 111 of the lower stage by a predetermined angle in the circumferential direction, thereby forming a skew structure.
However, a rotor and stator structure, to which the skew structure described is applied, has a problem in that a variation magnitude of torque is changed depending on a magnitude of load applied to the rotor by an electromagnetic force generated by an applied current so that it is impossible to optimize noise and vibration in various load conditions.